In vitro and in vivo regulation of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase isozymes from Chenopodium rubrum. II. In vitro modulation of the isozyme pattern

Isozymes of chloroplast glyceraldehyde‐3‐phosphate dehydrogenase (GPD, EC 1.2.1.13) from Chenopodium rubrum were separated using inverse discontinuous ammonium sulphate gradient solubilization. Leaves were extracted at the 9th h of light and the 9th h of darkness of a 12 h light/12 h dark cycle. The ratio of “NADP‐GPD I” to “NADP‐GPD II” varied with the light/dark cycle. However, the “light” isozyme pattern could be obtained from “dark” plants by including NADP + or NAD + kinase in the extraction buffer. Similarly, the “dark” isozyme pattern was produced in “light” plants extracted in the presence of NAD + . Pyridine nucleotides had no effect on the separated, purified isozymes. It is concluded that differential binding of the isozymes at the moment of extraction to pelletable material in the crude extract determines the isozyme pattern, and that this binding is regulated by the pyridine nucleotide ratio.